Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended																																																						3 Months Ended
	Mar. 31, 2013 VIE		Dec. 31, 2012		Mar. 31, 2013 Commercial Agreement Variable Interest Entities [Member]		Dec. 31, 2012 Commercial Agreement Variable Interest Entities [Member]		Mar. 31, 2013 Equity Method Investment Variable Interest Entities [Member]		Dec. 31, 2012 Equity Method Investment Variable Interest Entities [Member]		Mar. 31, 2013 Letter of Credit [Member]	Dec. 31, 2012 Letter of Credit [Member] Maximum [Member]	Mar. 31, 2013 Letter of Credit [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Dec. 31, 2012 Letter of Credit [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Mar. 31, 2013 Letter of Credit [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Dec. 31, 2012 Letter of Credit [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Mar. 31, 2013 Investments [Member]	Dec. 31, 2012 Investments [Member] Maximum [Member]	Mar. 31, 2013 Investments [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Dec. 31, 2012 Investments [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Mar. 31, 2013 Investments [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Dec. 31, 2012 Investments [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Mar. 31, 2013 Contract Intangible Asset [Member]	Dec. 31, 2012 Contract Intangible Asset [Member] Maximum [Member]	Mar. 31, 2013 Contract Intangible Asset [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Dec. 31, 2012 Contract Intangible Asset [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Mar. 31, 2013 Contract Intangible Asset [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Dec. 31, 2012 Contract Intangible Asset [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Mar. 31, 2013 Payment Guarantee [Member]	Dec. 31, 2012 Payment Guarantee [Member] Maximum [Member]	Mar. 31, 2013 Payment Guarantee [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Dec. 31, 2012 Payment Guarantee [Member] Maximum [Member] Commercial Agreement Variable Interest Entities [Member]	Mar. 31, 2013 Payment Guarantee [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Dec. 31, 2012 Payment Guarantee [Member] Maximum [Member] Equity Method Investment Variable Interest Entities [Member]	Mar. 31, 2013 Net assets pledged for Zion Station decommissioning		Dec. 31, 2012 Net assets pledged for Zion Station decommissioning Maximum [Member]		Mar. 31, 2013 Net assets pledged for Zion Station decommissioning Maximum [Member] Commercial Agreement Variable Interest Entities [Member]		Dec. 31, 2012 Net assets pledged for Zion Station decommissioning Maximum [Member] Commercial Agreement Variable Interest Entities [Member]		Mar. 31, 2013 Net assets pledged for Zion Station decommissioning Maximum [Member] Equity Method Investment Variable Interest Entities [Member]		Dec. 31, 2012 Net assets pledged for Zion Station decommissioning Maximum [Member] Equity Method Investment Variable Interest Entities [Member]		Mar. 31, 2013 Variable Interes tEntity Primary Beneficiary [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member]	Dec. 31, 2012 Baltimore Gas and Electric Company [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member]	Mar. 31, 2013 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]	Mar. 31, 2012 Baltimore Gas and Electric Company [Member] RSB Bond Co LLC [Member]
Consolidated Variable Interest Entities Disclosure [Abstract]
Current assets	$ 551		$ 550																																															$ 491	$ 519	$ 52	$ 30
Noncurrent assets	1,947		1,802																																															1,918	1,762	0	0
Total Assets	2,498		2,352																																															2,409	2,281	52	30
Current liabilities	575		685																																															492	613	76	71
Noncurrent liabilities	986		837																																															693	532	265	265
Total Liabilities	1,561		1,522																																															1,185	1,145	341	336
Deferred tax assets	0		0																																														116
Deferred tax liabilities																																																	59
Remittance of payments received from customers for rate stabilization to BondCo.																																																							22	20
Parental guarantee provided																																																				75		75
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of Variable Interest Entities not consolidated by equity holders	9
Number Of Variable Interest Entities Consolidated	5
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	698	[1]	740	[1]	360	[1]	386	[1]	338	[1]	354	[1]
Total liabilities	281	[1]	333	[1]	186	[1]	219	[1]	95	[1]	114	[1]
Our ownership interest	98	[1]	97	[1]	0	[1]	0	[1]	98	[1]	97	[1]
Other ownership interests	319	[1]	310	[1]	174	[1]	167	[1]	145	[1]	143	[1]	1						78						8						5						49	[2]
Our maximum exposure to loss														5	1	5	0	0		77	0	0	78	77		8	8	8	0	0		5	0	0	5	5			50	[2]	49	[2]	50	[2]	0	[2]	0	[2]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information Footnotes [Abstract]
Gross pledged assets	580		614																																															580	614
Pledged assets liabilities offset	$ 531		$ 564																																															$ 531	$ 564

[1] These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

[2] These items represent amounts on Generation’s and Exelon’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $580 million and $614 million as of March 31, 2013 and December 31, 2012, respectively; offset by payables to ZionSolutions LLC of $531 million and $564 million as of March 31, 2013 and December 31, 2012, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.